What is an essential feature of the 'AABA' song form?

The 'AABA' song form is characterized by its structure, which indeed involves alternating between two distinct melodic ideas, commonly referred to as A and B sections. In this format, the 'A' sections typically present a theme or lyrical content that is revisited and is often musically symmetrical, promoting familiarity. The 'B' section, often referred to as the bridge, provides contrast, both in melody and lyrical content, which helps to create interest and variation in the song.

The 'AABA' form is a classic format in many genres, especially in jazz and popular music, allowing for the exploration of a central theme (A) and a contrasting middle section (B) before returning to the thematic material (A) again. This cyclical nature is fundamental to how the form delivers emotional and musical continuity while also introducing some variation through the bridge.

Other options do not align with the structural essence of the 'AABA' form; it does not contain three distinct verses, nor does it focus on repetitive lyrics throughout, and it definitely does not consist of six verses, as the 'AABA' form is much more concise and specific in its design.